In recent wireless communication, a variety of methods have been proposed to increase a data communication demand and support a data service with a large amount of data. In order to increase a data communication demand and support a data service of a large amount of data, communication needs a high data rate. In order to achieve a high data rate, it is effective to use broadband frequency resources. However, most of the range of frequency resources, i.e., frequency bands from hundreds of MHz to a few GHz, have already been used for services by various service providers and systems as well as cellular systems. Therefore, it is not easy to secure additionally available frequency resources in the bands.
Recently, high carrier frequency bands which can easily secure an available frequency resource of a broadband have been allowed for the use of cellular system services. The higher the carrier frequency the shorter the transmission distance of signals, and this reduces the service coverage. Considering the feature, base stations of a cellular system use a beam-forming technology.
Beam-forming can efficiently extend the transmission distance of signals and the service coverage. Beam-forming refers to a technique that allows one transmitter to focus the transmission direction of signals on a particular direction using one or more array antennas or horn antennas. The beam-forming technology transmits signals in a corresponding direction to an increased transmission distance and decreases signals received from directions other than the corresponding direction, thereby reducing interference with unnecessary signals.
Although conventional communication signals extends a service coverage area and reduces an amount of interference using beam-forming, it needs to determine respective beams of the transmitter and the receiver in direction and in shape, in order to use an optimal channel.